PHP | DOMDocument validate() Function

<?php

// Create a new DOMDocument
$doc = new DOMDocument;

// Load the XML with DTD rule to have
// a root element with first, second,
// and third as its three children
$doc->loadXML("<?xml version=\"1.0\"?>
<!DOCTYPE root [
<!ELEMENT root (first, second, third)>
<!ELEMENT first (#PCDATA)>
<!ELEMENT second (#PCDATA)>
<!ELEMENT third (#PCDATA)>
]>

<!-- Create a XML following the DTD -->
<root>
<first>Hello</first>
<second>There</second>
<third>World</third>
</root>");

// Check if XML follows the DTD rule
if ($doc->validate()) {
    echo "This document is valid!\n";
}
?>

<?php

// Create a new DOMDocument
$doc = new DOMDocument;

// Load the XML
$doc->loadXML("<?xml version=\"1.0\"?>
<!DOCTYPE root [
<!ELEMENT root (one, two, three)>
<!ELEMENT one (#PCDATA)>
<!ELEMENT two (#PCDATA)>
<!ELEMENT three (#PCDATA)>
]>
<!-- Create a XML voilating the DTD -->

<root>
<one>Hello</one>
<two>World</two>
</root>");

if (!$doc->validate()) {
    echo "This document is not valid!";
}
?>